In this paper, a novel numerical temporal convolution method is presented to calculate the convolutions between the retarded-time potentials and temporal basis functions (or its integration, derivation) in marching-on-in-time (MOT) solver. This approach can smooth and eliminate the singularity of integrated functions by variable substitution. It can also effectively control the precision of numerical quadratures over the surface of the source distribution. Thus it is suitable for more types of temporal basis functions including non-piecewise polynomial functions. Numerical results demonstrates that this improved method can ensure the accuracy and late time stability of the MOT solver with different types of temporal basis functions.

The dispersion diagram of infinite periodic structures is useful for the practical design of waveguide filters. Analyzing the pass- and stop-bands (gaps) in the dispersion diagram of a unit cell, it is possible to generate a finite structure with a very similar electrical response. However, the truncation of the infinite periodic structure degrades the pass-band performance. In this paper, these impairments are overcome by means of suitable waveguide tapers matching the impedance of the periodic structure to the access ports. As a result, the analysis and design of practical low-pass filters, derived from passive structures based on Electromagnetic Band-Gap (EBG) waveguides periodically loaded with metal ridges, are successfully addressed. According to these procedures, a five-order and an eight-order EBG low-pass filters are obtained after an optimization step. Measurements of a manufactured prototype fully validate the proposed approach.

We propose a wideband multifunctional device which combines a linear-to-circular polarization convertor with focusing metasurface. The proposed design is built by a novel dual-layered metal cross and cross ring unit cell which exhibits satisfying performance for controlling the reflecting phase of the electromagnetic wave polarization-independently. The device is illuminated by a Vivaldi antenna, and the functions of polarization conversion and gain enhancement have been simultaneously achieved in the band of 9.12-10.2 GHz. In addition, the polarization helicity of the system can be reconfigured by rotating the feed antenna. The device has not only greatly presented the flexibility and superiority of the metasurface in steering the electromagnetic waves, but also promoted the development of the multifunctional metasurface.

Target-supporting metal pylon predominantly contributes to background scattering in radar cross section measurement. The separation of scattering from the target and background demands stable background scattering. However, target translation creates variations in metal pylon deformation and changes its scattering, which yields errors in background separation. Analyzing the relationship between the structural parameters of metal pylon and the error caused by its deformation is necessary to reduce errors. A simplified mapping of the relationship is deduced according to the mechanical and electromagnetic theories involved. The approach combines geometrical theory of diffraction for pylon scattering and numerical integration in calculating the deflection of metal pylon to determine the variation of metal pylon scattering, and calculates error in the circle fitting caused by the variation. Simulations with commercial software are employed to verify the efficiency of the numerical model. Although it is slightly contaminated by target-pylon interaction, the approach is 800 times faster than the software simulation. An example of optimization and analysis is provided to demonstrate the trends of optimum structural parameters and fitting error within different pylon weight limits. Such an example proves that the approach can overcome the deficiency of traditional analysis which separately assesses the mechanical and RCS performances of metal pylon.

This paper presents a new property of maximally-at filter prototype coefficients. The property can be used to relate the summation of all the coefficients to an elegant expression which only includes the first coefficient. This property is then used to calculate the increase in insertion loss of this type of filters in the presence of dissipative losses due to elements/resonators finite quality factors. This presented equation for the excess loss is very convenient and does not require referring to the prototype element value table. The property is also used to show that the group delay of a maximally-at lowpass filter at ω = 0 rad/sec is only a function of the first element value of the prototype filter. Finally, a commercial circuit simulation tool is used to generate examples to verify the accuracy of the presented analytical equations. Additionally, the results are compared to expressions found in classical literature.

Synthetic aperture radar (SAR) system has inherent constraints between high azimuth resolution and wide swath width. Achieving more phase center samples is one of the key solutions to resolve this limitation. By multiple N transmitting and N receiving channel concept, an increased resolution or a widened swath width could be obtained. In this paper, comprehensive analysis for shifting multiple-input multiple-output (MIMO) SAR system is presented. System resolution enhancement has been demonstrated based on the distributed target simulation by a factor of N compared to conventional displaced phase center antenna (DPCA) system.

In this article, we study the far-field trapping behavior of dielectric nanospheres with diameter of 200 nm by utilizing a plasmon enhanced far-field nanofocusing lens. Based on our high effectnanofocusing circular plasmonic lens, such a far-field plasmonictrap is constituted by illuminating with a laser to form a sharper focus (subwavelength) due to a constructive interference of cylindrical surface plasmon wave. The nanoparticles can be steadily trapped in the far-field focal region (4.4λ) with an optical force to nanonewton (-4.76 nN) order, and the required optical power is less than 0.5 W. Compared with other surface plasmon tweezers, the proposed far-filed plasmonic tweezers can not only avoid physical contact with the trapped particles to prevent contamination and reduce thermal damage effects due to metal absorption, but also enable the easy trapping and manipulation of nanosizedielectric particles owing to nanonewton scale forces.

This work proposes a modified Volterra-based series suitable for the low-pass equivalent behavioral modeling of radio frequency power amplifiers (RFPAs) for wireless communication systems. In a Volterra-based series, the instantaneous sample of the complex-valued output envelope is calculated by the sum of products that depend on the instantaneous and past (up to the memory length M) samples of the complex-valued input envelope. To comply with the constraints imposed by the bandpass behavior of RFPAs, the derivation of the proposed model starts from a general Volterra-based series given by the sum of contributions that include exactly one complex-valued information multiplied by a varying number (ranging from zero up to one less than the polynomial order truncation P) of real-valued amplitude components. A first reduction in the number of parameters is then performed by retaining only the one and two dimensional contributions. A second reduction in the number of parameters is finally achieved by introducing a third truncation factor S. In fact, if this additional truncation factor S is set equal to P-1, the proposed model contains all the two dimensional contributions. Moreover, when S is set equal to 0, the proposed model reduces to the largely adopted generalized memory polynomial (GMP) model. The proposed Volterra-based series retains the important property of being linear in its parameters and, in comparison with previous Volterra-based approaches, can provide a better compromise between number of parameters and modeling error. The proposed model is then compared with the GMP model in a scenario of same number of parameters. When applied to the modeling of input-output data obtained from a circuit-level description of a GaN HEMT Doherty PA excited by a LTE OFDMA signal, the proposed model reduces the normalized mean square error (NMSE) by up to 3.4 dB. Additionally, when applied to the modeling of input-output data measured on a GaN HEMT class AB PA excited by a WCDMA signal, the proposed model reduces the NMSE by up to 1.3 dB.

Guided and leaky modes for a circular dielectric rod are analyzed in detail in this paper. By considering the field distributions, these modes are well defined and classified. The relations for the mode solutions using different types of special functions and Riemann sheets are figured out. Further, completed forms of characteristic equations used to solve different modes are presented explicitly. Asymptotic expansion method and Lambert W function are employed to derive the initial guesses around cutoff frequency, low frequency limit and high frequency limit for both TM and TE cases. The behaviors of complex transverse attenuation constants for proper and two types of improper modes with different cases are presented with some modes not shown in literatures.

In classical electromagnetics textbooks, the microwave circuits such as circulators, couplers, and filters are solved by non-systematic approaches such as even-odd mode analysis. Hence an electrical engineering student coming from the conventional circuit theory background encounters difficulties in understanding and solving microwave circuits. In this paper, we propose a modified node voltage analysis method in which the circuit branches are represented by their forward transmission matrices so that the electromagnetic wave propagation is taken care of. The Kirchhoff's current rule, tailored for high frequencies, is applied to formulate the simultaneous node voltage equations which are subsequently solved by matrix inversion. The proposed forward transmission matrix (FTM) method is applied to evaluate the S-parameters of some well-known microwave devices including the recently-developed metamaterialbased circuits. The FTM node analysis is a natural extension of the classical node analysis which is taught in the early stages of an Electrical Engineering program. Hence we anticipate that the proposed method will ease up the conceptual transition of electrical engineering students and academicians from the low-frequency alternating current circuits to high frequency RF and microwave circuits.

In this letter, a four-layer transmitarray operating at 9.5 GHz is designed using a double-petal loop element as the unit cell. A configuration of the double-petal loop elements is used to increase transmission phase variation while maintaining a wide transmission magnitude bandwidth of the unit cell, and a full transmission phase range of 360° is achieved for a transmission magnitude equals to or better than -2.4 dB. Furthermore, the oblique performance of the unit cell is also good. Then, a prime-focus 676-element microstrip transmitarray with the proposed element is fabricated and measured. The highest measured gain is about 22.15 dBi at 9.8 GHz, resulting in a 31% aperture efficiency. The antenna bandwidth of 10.2% (from 9.3 to 10.3 GHz) for 1 dB-gain is achieved in this design.

The radial suspension force with a new structure of a bearingless induction motor based on single winding is researched. Compared to the conventional double-winding structure of bearingless induction motor, torque and suspension forces are produced with a single-winding system. Bearingless induction motor is a nonlinear, multi-variable and strong coupling system. It is difficult to obtain an accurate mathematical model on the radial suspension force. So the research method about radial suspension force of a single-winding bearingless induction motor is proposed, based on two fundamentals. Firstly, a new structure and operation principle of a single-winding bearingless induction motor is introduced. Then the air-gap flux density distribution of the single-winding bearingless induction motor is analyzed in detail. The accurate mathematical model of radial suspension force is deduced by using two-fundamental wave method and Maxwell's stress tensor method. Secondly, according to the transient analysis of the single-winding bearingless induction motor which its speed is 6000 r/min, by finite element method (FEM), the component of radial suspension force in x-axis and y-axis is obtained by FEM simulation analysis. The calculation results used by FEM and the theoretical calculation results of mathematical model used by two fundamental wave method have been compared. Thirdly, an experimental prototype is produced, and suspension experiment of prototype is carried out. Then measured result of radial suspension force is analyzed. The analysis results show that the prototype has excellent suspension characteristics, and the mathematical model of radial suspension force based on two-fundamental wave method has low error and high precision.

This paper presents the design and development of Koch fractal dipole antenna for wearable applications at 450 MHz. Common jeans cotton is used as a flexible substrate material having a dielectric constant of 1.6 for the design and fabrication of the proposed antenna. Increasing the number of iterations increases the number of sections, which eventually results in 32% reduction in size. Size miniaturization is obtained using second iteration Koch geometry with the antenna bandwidth of 10%, and the return loss of -25 dB is achieved under the flat condition. The investigations are to characterize the antenna not only in flat condition, but also under different bendings and crumpling conditions. The proposed Koch fractal antenna is close to the proximity of the body, and the absorption of electromagnetic power on human body is also examined. It is found that the Specific Absorption rate (SAR) is much below a safety level of 0.119 W/kg and hence suitable for wearable applications.

In this paper, a new coplanar waveguide (CPW) fed ultra-wideband (UWB) planar monopole antenna with dual band-reject characteristics is proposed. Two resonators of different lengths are employed at the bottom layer to create two notches at the frequency of interest. The proposed fabricated antenna works from 2.8 to 11.34 GHz with two notched bands which cover the WLAN (5.725-5.825 GHz) and ITU (8.025-8.4 GHz) bands. The proposed antenna is fabricated and measured for verification purposes. Good agreement between the measurement and simulation is found.

To visualize eddy current distribution (ECD) of an arbitrarily shaped coil arranged parallel to a moving conductor slab, an exact theoretical solution is derived using an analytical method based on the double Fourier transform method. The arbitrarily shaped coil is regarded as a plane coil of a single turn, and both DC and AC excitation currents can be applied. Furthermore, ECD charts are obtained when the conductor slab is moving. We calculate some examples with respect to a circular coil, rectangular coil, and triangular coil and show the effect of coil excitation frequency and speed of the conductor on ECDs. Results show that the eddy current generated in the moving conductor slab is composed of current induced by the excitation frequency and conductor speed.

An ultra-compact chiral metamaterial (CMM) using triple-layer twisted split-ring resonators (TSRRs) structure was proposed, which can function as a multi-band circular polarizer. This ultra-compact structure can convert an incident linearly y-polarized (x-polarized) wave propagating along the -z (+z) direction to the transmitted left circularly polarized (LCP) waves at 7.28 GHz, 13.22 GHz and 15.49 GHz while the right circularly polarized (RCP) waves are at 9.48 GHz. In addition, the large polarization extinction ratio (PER) of more than 20 dB across four resonance frequencies can be achieved. The experiment results are in good agreement with the numerical simulation results. The surface current distributions of the structure are analyzed to illustrate this linear to circular polarization conversion. The unit cell structure is extremely small both in longitudinal and transverse directions. Good performances and compact design of this CMM suggest promising applications in circular polarizers that need to be integrated with other compact devices.

A new direction-of-arrival (DOA) and power estimation method of unknown number of source signals is proposed. The direction and power of coherent and/or non-coherent signals are estimated by controlling the roots of the array polynomial on the unit circle. The genetic algorithm is used to find the phases of the array polynomial roots that minimize the array output power. The pseudo-spectrum is obtained by phase rotation of the estimated roots, and the real power spectrum is derived from the pseudo-spectrum and the array factor. The results indicate that the direction of arrivals, power of the signals, and number of source signals are estimated from the real power spectrum.

A wideband dual-polarized dipole antenna is presented using the differential feed technique. The proposed antenna consists of two horizontal bow-tie dipoles and four vertically oriented meandering strips. Two pairs of differential-fed L-shaped microstrip feed lines are used to excite the antenna. Due to the differential-fed technique, the cross polarization level can be reduced to -35 dB. With the introduction of the meandering strips connecting the radiating patch to the ground plane, the height of the antenna is about 0.102λ₀. A parametric study is performed to provide information for designing and optimizing such an antenna. The proposed dipole antenna has been fabricated and measured. The impedance bandwidth of 48.3% (S₁₁ < -10 dB) from 2.57 GHz to 4.21 GHz is achieved. The measured isolation between the feeding ports is better than 30 dB over the operating band. Moreover, the antenna has a compact structure and good unidirectional radiation pattern, making it conveniently integrated with microwave differential circuits and applied in the base station systems.

To reduce the radar cross section (RCS) of a target, plasma coating on perfectly electric conducting plate is studied in this paper. Nonuniform helium plasma produced by a minitype solid rocket engine is with collisional and unmagnetized. Energy excited for generating helium plasma is investigated. Based on the collisional, unmagnetized, and cold plasma model, backscattering RCS is computed by using finite-difference time-domain method. Principle of RCS reduction is explained. To find minimum input energy while RCS reduced, relationship between input power and RCS reduction is discussed, and numerical optimization is also implemented. We can identify optimal parameters and choose the best electron density profile under condition of given input power level.

To improve absorbing properties of phase-modulated surface (PMS), the multi-active-layer PMS composed of multiple active frequency-selective surface (AFSS) layers and one background plane is theoretically studied using time-modulation theory in this paper. The optimization of PMS's switching scheme using differential evolution (DE) algorithm is also proposed for minimizing scattering echo energy at the incident frequency. We provide analytical formulation for the scattering problem and obtain the angular scattering pattern of PMS after optimization. Simulation results indicate that the optimized switching scheme is beneficial for reducing the spatial coverage of scattering echo at incident frequency. This coverage can be further confined by the increasing number of active layers in PMS. Furthermore, it is shown that floor effect appears when the number of active layers reaches a certain value, which limits the PMS structure conversely.